Roofing materials for covering large buildings are customarily available in sheets having a length up to several hundred feet and a width of from about three feet to about 50 feet. During installation, the roofing membranes are generally primed at their overlapped edges, before being joined together using an adhesive composition to form a weather-impermeable sealing barrier. In the past, solvent-based adhesives (neoprene and butyl-based) have been used to bond flat rubber sheets together. However, these adhesives have limited storage-life, and are highly toxic and flammable. The application of solvent-based adhesives via paint brushes often leaves streaks or coatings of uneven thickness and are known to reduce bond strength between the adhesive and the rubber sheeting. Also, solvents are environmentally undesirable and subject to increasing governmental regulation. Preformed adhesive tapes are generally preferred because they require less time and skill to install and eliminate the risk of exposure to hazardous, volatile, organic solvents generally found in solvent-based adhesives.
Efforts have been made in the art to develop better adhesive tapes which may be easier to apply to the overlapped edges of the rubber substrate, and which provide a long term capability to withstand moisture and heat aging. For example, Streets, U.S. Pat. No. 4,640,730, teaches the use of a styrene-butadiene block copolymer mixed with a hydrocarbon resin as a tape adhesive for bonding together EPDM and butyl rubber based flat rubber roof sheeting. Additionally, other attempts have been made in the art to develop adhesive tapes which may be easier to install and provide a long term water-tight barrier. For instance, Chiu, U.S. Pat. Nos. 4,588,637, 4,855,172 and 5,095,068, teaches a roofing adhesive tape utilizing butyl rubber compositions made by incorporating carbon black, a plasticizer, one or more tackifying resins and at least one curing agent in a blend of butyl rubber elastomers. The butyl-based tapes described by Chiu require additional fabrication steps involving precuring of the rubbery composition prior to application of the tape. U.S. Pat. No. 4,601,935 issued to Metcalf et al., disclosed an elastomeric polymer-based adhesive seaming tape comprising a carbon black reinforced lightly cured blend of butyl rubber and polyisobutylene.
Kakehi, U.S. Pat. No. 4,404,056, teaches a cold vulcanizable adhesive tape having a Mooney viscosity of from about 5 to 25 which includes one or more rubbery polymers, a vulcanizing agent, a vulcanization accelerator, an adhesive agent and a softening agent. The tape is positioned between overlapping sheets of unprimed flat roof sheeting, and the sheets are pressed together with a roller or the like. Other patents related to the use of tape compositions include, for example, Callan, U.S. Pat. No. 3,976,530, which discloses the use of blends of crosslinkable butyl rubber and polyisobutylene. The curing ingredients were incorporated in the non-crosslinkable polymer in order to prevent a premature reaction between the vulcanizing agent and the crosslinkable butyl rubber (two-component polymer tape) prior to extrusion of the tape product. Other patents include U.S. Pat. Nos. 4,379,114 to Fujuki et al., and 4,581,092 to Westley each mentioning the use of uncured, preformed, adhesive seaming tape compositions which contain EPDM, butyl rubbers, and mixtures thereof.
Such uncured, but curable, seaming tape compositions generally fall into one of three categories: (1) those containing fast-acting, cold-vulcanizable cure systems, (2) those containing heat-activated cure systems, and (3) those containing slow reacting, cold-vulcanizable cure systems. In the case of the seaming tape adhesive compositions having fast-reacting, cold-vulcanizable cure systems, it is generally necessary to blend and extrude the composition on-site and immediately thereafter apply the extruded adhesive tape composition to the roofing membranes which are to be joined together in order to prevent premature curing which can adversely affect the adhesive properties of such compositions. The seaming adhesive tape compositions containing heat-activated cure systems have the obvious disadvantage of requiring additional on-site apparatus and steps to thermally initiate the cure process. For the adhesive seaming tapes having slow acting, cold-vulcanizable cure systems, it is possible to preform the tape off-site and then install the tape to join roofing membranes without requiring additional equipment or steps to thermally initiate and propagate the cure. However, such slow-curing adhesive compositions do not generally exhibit good initial adhesion, and can take several days or even weeks to achieve good adhesion, particularly if they are used in cold weather.
However, the need still remains in the art for effective adhesive tape compositions and methods of application for use in adhering together the primed overlapped seams of flat rubber sheets which provides not only ease of application and good seam strength, but also wherein a suitable bond is formed between the primed overlapped edges of two flat rubber sheets.